Process of degreasing aluminum and magnesium surfaces



Patented July 1, 1947 PROCESS OF DEGREASING ALUMINUM AND MAGNESIUM SURFACES Edwin I. Plueddemann, Woodbridge, N. 3., and- Richard ltatliman, Westvaco Chlorine Decatur, Ind., Products Corporation, New

assirnorsto York, N. Y., a corporation of Delaware No Drawing. Application April 27, 1945, Serial No. 590,738

3 Claims. 1

This invention relates to process of degreasing aluminum and magnesium surfaces with chlorinated hydrocarbons containing an inhibitor of corrosion.

In many practical operations or commercial applications halogenated hydrocarbons a such or as ingredients of various compositions come in contact with metals and frequently exert a corrosive action thereon. For example, when halogenated hydrocarbon solvents, such as carbon tetrachloride, trichlorethylene, ethylene chloride, chloroform, pentachlorethane, etc., are brought into contact with metal surfaces, particularly light metals, such as aluminum and magnesium, in degreasing operations undesirable corrosion results. In the degreasing of Dow metal, which is a 95% magnesium alloy, by the use of a degreasing agent composed of commercial trichlorethylene and an alcohol, and also in the use of the same type of degreasing agent in contact with aluminum, undesirable corrosion has been found to occur.

Likewise, when commercial trichlorethylene compositions or other chlorinated hydrocarbons, such as carbon tetrachloride, are incorporated in metal containers or containers having metal parts which are corroded by such chlorinated hydrocarbon materials, we have found that not only are the containers corroded and thereby weakened or rendered unsuitable for subsequent use, but the compositions are also contaminated to a degree which makes them unsuited for many purposes. For instance, chlorinated solvents which have been subjected to metal-induced decomposition are generally not suitable for use as cleaning fluids.

We have found that the corrosive action of the halogenated hydrocarbon solvents, such as those mentioned above, on metals, and particularly light metals, may be substantially diminished by the incorporation of a small percentage, say less than 1% by weight, of an amide of formic acid. Larger percentages may be used but the added protection, if any, usually does not warrant the added expense. In general, the tendency of the chlorinated hydrocarbon solvents to corrode metals is decreased most markedly by the incorporation of formamide. At times, however, it is preferable to use certain N-substituted amides of formic acid such as formanilide, methyl formamide, and ethyl formamide, which are usually more soluble in chlorinated hydrocarbon solvents than formamide.

The power of formamide to retard the corrosive action of chlorinated hydrocarbon compositions is well illustrated in the diminution in the corrosive action of a degreasing agent consisting of commercial trichlorethylene containing a small percentage of a compatible alcohol such as butyl alcohol. When Dow metal, a magnesium alloy, is immersed in the foregoing degreasing agent and subjected to reflux temperatures for the solvent, a heavy corrosion takes place within five hours. Under the same conditions, the same metal immersed in the same degreasing agent containing 0.05% by weight of formamide remains in excellent condition after ninety-six hours. Under reflux temperatures for the solvent, the addition of the same percentage of formanilide to the trichlorethylene degreasing composition protects the Dow metal against corrosion for a period of forty-eight to seventy-two hours and N-ethyl formamide and N-methyl formamide protect it for a period of twenty-four hours and of eight to twenty hours, respectively.

It has been observed in the utilization of degreasing compositions containing trichlorethylene that the formamide, in addition to protecting the metal from corrosive action of the degreasing composition, acts as a reducing agent for peroxides which are known corrosives to metals present in commercial trichlorethylene. Thus formamide is especially valuable for reducing the corrosive action of degreasing agents. dependent upon the solvent action of commercial trichlorethylene.

The incorporation of formamide in compositions containing carbon tetrachloride seems to serve a dual purpose when such compositions come in contact with aluminum, namely, as an anti-corrosive for the metal and a stabilizing agent for the chlorinated hydrocarbon. For example, carbon tetrachloride will catalytically decompose in the presence of aluminum at reflux temperatures under substantially anhydrous conditions within one-half an hour while the same compositions containing 0.2% of formamide exert no appreciable decomposition or corrosive action after ninety-six hours of contact with aluminum. The same percentage of methyl formamide shows similar stabilizing and corrosion inhibiting properties for a period of forty-eight hours and N-ethyl formamide for a period of eight to twenty hours.

The foregoing discussions have related to reductions in the corrosive action of compositions containing or based upon chlorinated hydrocarbons when in contact with light metals, such as those having a density below 4. When such compositions are in contact with the light metals their corrosive action is substantially less than that of similar composition known to us containing known commercial corrosion inhibitors. It should be understood, however, that the corrosive action of the compositions of this invention is also substantially reduced by the inclusion of our corrosion inhibitors when they are in contact with other metals such as the metals found in various containers and the like.

It will be understood that metal is used herein in its generic sense and includes both elemental metal and various alloys.

Many modifications in the teachings of this invention will occur to those skilled in the art and yet be within the scope of the invention which i defined by the appended claims.

We claim:

1. An improved process of degreasing surfaces of light metals of the group consisting of aluminum and magnesium with chlorinated hydrocarbon solvents of the group consisting of carbon tetrachloride, trichlorethylene, ethylene chloride, chloroform and pentachlorethane, which are normally subject to decomposition in the presence of such metals, which comprises contacting such metal surfaces with a degreasing composition consisting essentially of said chlorinated hydrocarbon solvents and formamide in a small quantity'suflicient to substantially inhibit said decomposition.

2. An improved method for degreasing aluminum with chlorinated hydrocarbon solvents of the group consisting of carbon tetrachloride and trichlorethylene, wherein said solvents are normally decomposed in the presence of aluminum or the aluminum is corroded by said solvents, I which comprises contacting the surfaces of the aluminum with a solvent composition consisting essentially of said chlorinated hydrocarbons and formamide in amounts of approximately 0.02% to 0.05% byweight of said solvent. 3. An improved method of degreasing a magnesium alloy with chlorinated hydrocarbon solvents of the group consisting of carbon tetrachloride and trichlorethylene, wherein said solvents are normally decomposed in the presence of the 95% magnesium alloy, or the 95% magnesium alloy is corroded by said solvents, which comprises contacting the surfaces of the 95% magnesium alloy with a solvent composition consisting-essentially of said chlorinated hydrocarbon and formamide in a quantity sumcient to substantially retard said corrosion and decomposition.

EDWIN P. PLUEDDEMANN.

RICHARD RATHMAN.

REFERENCES CITED The following references are file of this patent:

UNITED STATES PATENTS of record in the 

